In an IoT (Internet of Things) system, it is necessary to exchange data with an enormous number of MTC (Machine Type Communication) devices connected to the network. Therefore, it is required to reduce the number of data messages from an enormous number of MTC devices or the number of control messages to an enormous number of MTC devices. To achieve this, a method of collectively transmitting messages to MTC devices regionally or constitutionally belonging to the same group is being examined. Non-patent literature 1 (TR 23.888) describes a technique of reducing the number of messages exchanged with MTC devices, avoiding network congestion, and saving resources by grouping devices in the same area or devices having the same function to collectively transmit messages to the same group.
Non-patent literature 2 (TR 23.887) describes some methods as group messaging methods. More specifically, a method of using a CBC (Cell Broadcast Center) and a CBS (Cell Broadcast Service), a method of using an MBMS (Multimedia Broadcast and Multicast Service), and a method of using IP (Internet Protocol) multicast are described. A group message from an SCS (Service Capability Server) is transmitted to MTC devices. If the MTC device cannot receive the group message for some reason such as a temporal failure of a wireless access network, the SCS is notified of it (action in response to group messaging), and executes processing such as retransmission, as needed.